Attachment devices exist for fixing EEG electrodes to a patient's scalp. These devices may use colloidal glue, adhesive tape or bandages. EEG electrodes may also be attached by incorporating them into web matrix helmets. Placing and removing these EEG electrodes from a patient's scalp is time consuming. The EEG electrodes are uncomfortable to wear and may loose signal contact during extended ambulatory monitoring.
Web matrix helmets are headpieces made of a webbing material. Web matrix helmets are fastened to the patient's head by means of a chin strap and/or a neck strap with scalp-pattern electrodes attached along the under-surface of the web material. Web matrix helmets cannot be used unobtrusively in ambulatory settings. Furthermore, each contact area on the patient's head must be thickly coated with an electrolytic gel to obtain good signal quality. Even with this preparation, since the electrodes themselves trap large quantities of hair between the electrode body and the scalp, there is a possibility for signal loss from any one electrode. Also, during the course of long-term monitoring, re-application of electrolytic gel is often necessary to maintain signal quality. Lastly, web matrix helmets do not fit all head shapes and sizes, making electrode placements problematic with some patients.
Scalp placement electrodes may also be attached to the patient by means of an adhesive paste. The electrode is pressed into a large amount of electrolytic adhesive paste or gel applied at the desired placement site, and then the electrode is taped in place to allow the adhesive to set. The electrodes are obtrusive, and a large amount of electrolytic gel is needed to maintain proper contact because the electrode-scalp interface tends to dry out through evaporation. In addition, adhesive-attached scalp electrodes cannot be used in most ambulatory settings because they tend to become dislodged during normal movement or activity. Finally, this type of placement entails a messy and time consuming clean-up.
Colloidal glues achieve stronger bonding between the electrode and the scalp, but their use is both time and labor intensive. In a typical application, electrolytic gel is applied to the patient's scalp, the electrode is seated and taped in place, and the colloidal glue is applied and allowed to dry. This process can take 7-15 minutes per electrode. Removing the electrode requires applying a solvent, and the patient is inconvenienced because the collodion remains in the hair. In addition, the collodion and solvents emit strong fumes, limiting their use to specially ventilated rooms. Also, because the collodion can bond to unintended surfaces, special care must be used not to touch any other material while gluing the electrodes in place. Lastly, many patients may experience scalp irritation due to sensitivity or allergic reactions to the collodion.